The increasing number of variant strains of infectious bronchitis are threatening the profit margins of commercial chicken producers worldwide, as mortality rates are high and the disease spreads quickly.
Speaking at the South African Poultry Association Congress in Johannesburg, Dr Sjaak de Wit from the Dutch Animal Health Service said some variants stay for a longer time, while others come and go and might reappear later. “Lately we’ve found that outbreaks are increasing and are more severe
despite normal vaccinations,” said Dr De Wit.
Signs that a chicken is infected include sneezing, gasping, nasal discharge and swollen head syndrome. The disease can also kill suddenly if untreated. These viruses decrease feed intake and growth, lower egg production, increase the ratio of second-grade eggs, decrease hatchability, damage the testes and cause false layers and intestinal problems.
As vaccines against each variant aren’t available, Dr De Wit advised that available vaccines be used optimally. “Consider revaccinating, but not too soon unless the first vaccination wasn’t well applied. A vaccination that’s given properly may give more cross-protection.”
When vaccinating young birds, homologous strains provide best protection against homologous challenges. Farmers must broaden cross-protection by repeating vaccination, preferably with vaccines of different protectotypes. Not every variant needs a special vaccine,” he said.
“Laying birds can be given inactivated vaccines (one or more infectious bronchitis variant antigens) to get higher antibody titres (related to higher protection),” said Dr De Wit. – Lindi van Rooyen
Source: farmersweekly.co.za
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